Wlodzimierz Umaniec is jailed for two years for vandalising a Mark Rothko painting worth over £5m at the Tate Modern, in what the judge called an "utterly unacceptable" attack.
Wlodzimierz Umaniec, 26, also known as Vladimir Umanets admitted criminal damage to the value of in excess of £5,000. But estimates suggest the restoration of the painting - worth between £5m to £9m - will cost around £200,000.
Umaniec, from Poland, claimed the act was a "yellowism", referring to the art movement he co-founded.
Judge Roger Chapple, at inner London crown court, told Umaniec: "Your actions on 7 October of this year were entirely deliberate, planned and intentional."
The court heard that Umaniec went to the gallery intending to put his "signature" on a picture, but decided to damage the Rothko painting, Black On Maroon, only at the time he saw it on display.
The gallery was then put into "operation shutdown", with people prevented from leaving or entering the building.
A visitor the gallery, Tim Wright, tweeted one of the first pictures of the vandalism just after the incident occured [see below].
The defaced painting was donated to the Tate in 1969 by Rothko himself.
Speaking about "yellowism", Judge Chapple said it was "wholly and utterly unacceptable to promote it by damaging a work of art" which he called a "gift to the nation".
He said it was "abundantly clear" that Umaniec was "plainly an intelligent man" and told the court he had described Rothko as a "great painter" in a letter he had written to him.
The judge also said the incident had led to galleries reviewing security arrangements at a cost to themselves and the taxpayer. "The effects of such security reviews is to distance the public from the works of art they come to enjoy," he said.
Outside court before the sentencing, Ben Smith, who called himself a "yellowist", attempted to explain the concept: "Everything is equal. Everything is art. Everything is a potential piece of yellowism."
Gregor McKinley, prosecuting, said: "Sotheby's has given Tate Modern a verbal estimate of pre-damage value of approximately between £5m to £9m."
He added: "The work required to restore this picture will be complex and lengthy. Complications to this work include the unique painting technique used by the artist and the fact the ink used by Mr Umaniec has permeated the paint layers and the canvas itself."
Mr McKinley said work to restore the painting will take about 20 months and cost "something around £200,000".
Gareth Morgan, defending, said it would take a "significant amount of effort, expert effort at that" to restore the "important, valuable piece of art".
Paintings by Russian-born artist Rothko often fetch tens of millions of pounds. Earlier this year, his Orange, Red, Yellow sold for £53.8m - the highest price paid for a piece of post-war art at auction.